Conventional medical analysis and therapy often involves use of a plurality of individual electrodes, each applied independently to an appropriate location on a subject's body by way of electrically conductive paste, and securing means such as a skin compatible adhesive. A relevant example of use is in the monitoring of Electrocardiogram (ECG) signals at precordial; and at left and right arm, and left Leg locations by independent electrodes in an Einthoven triangle configuration.
Further, it is known to apply individual non-invasive precordial electrodes to a subject's chest to allow not only the acquiring of ECG data, but to allow defibrillation of fibrillating hearts and to allow the pacing of arrested hearts and the like.
A problem which presents in the use of such independent electrodes, however, is that reliable, repeatable placement upon a subject's body is difficult. For instance, it is generally accepted that a majority of the errors encountered in acquiring ECG data is caused by improper electrode placement by medical technical staff.
Of relatively recent development are flexible electrode pads which comprise a multiplicity of electrodes affixed thereto in an appropriate pattern for use in medical analysis and/or therapy. For instance, a Patent to Manoli, U.S. Pat. No. 4,583,549 describes an ECG electrode pad in which six conductive discs are plated and etched on a flexible adhesive pad in a clinically conventional predetermined pattern effective for precordial ECG electrode placement. Reproducible attachment of said six electrodes to a subject's chest in the proper arrangement for use with standard ECG machines is thus made possible by a single application of an electrode pad of an appropriate size for use with any subject. However, it would seem that the Manoli system would require a host of numerous sized electrode pads to accommodate subjects of different sizes as the Claims recite rather strict electrode placement criteria which are referenced with respect to a subject's body. A single electrode pad would not meet said requirements on subjects of different sizes. A Patent, U.S. Pat. No. 4,121,575 to Mills et al. describes a multiple electrode device for application to a subject's chest, formed in stretchable non-conductive material having apertures in the V1-V6 positions. The capability for stretching the material is held to allow accurate positioning of V1-V6 electrodes on subjects of differing body size. A Patent to Groeger et al., U.S. Pat. No. 4,957,109 describes an electrode assembly comprising right and left arm and leg leads, and precordial leads all affixed to a common structure. The arm and leg leads do not affix to a subject's chest during use. The Mills et al. and Groeger et al. systems do not serve to maintain a relatively fixed positioning of electrodes therein during use, and it is noted that movement between electrodes during use frequently causes confounding noise generation in electrocardiography systems. Another Patent, U.S. Pat. No. 5,327,888 to Imran describes a precordial electrode strip which is supplied with detachable RA, LA and LL limb leads, which detachable limb leads are applied to subject limbs in use.
Patents to Way et al., U.S. Pat. Nos. 4,955,381 and 5,080,099 describe multiple conductive polymer pad containing electrodes for performing multiple electrical physiological functions from a set of electrodes with respect to a subject, at or about the same time, such as defibrillation, pacing and monitoring. Other Patents which disclose multiple electrode assemblies are U.S. Pat. No. 4,328,814 to Arkans and U.S. Pat. No. 5,191,886 to Paeth et al. These Patents each describe a plurality of electrodes configured in a physically seriesed configuration with conductive leads to various physically seriesed contacts, present at one end thereof. In addition, a Patent to Collins, U.S. Pat. No. 3,612,061 describes a porous sheet of elastic material which supports an array of electrodes adapted to contact a wearer's skin, and U.S. Pat. No. 5,184,620 to Cudahy et al. describes an electrode pad system comprised of a multiplicity of electrodes which are utilized in defibrillation and pacing scenarios as directed by an on-line computer driven analysis and electrical energy application system, which system distributes electrical energy to appropriate sets of said multiplicity electrodes in response to subject needs.
Continuing, it is to be understood that particularly appropriate materials in which to form an electrode pad with a plurality of ECG monitoring electrodes present therein are hydropolymers. This is because hydropolymers can be pliable, self-adhesive and compatible with maintaining the requisite hydration of subject skin to which they affix during prolonged use. The pliable property makes hydropolymers exceptionally well suited for application to unpredictable irregularities of various subject's chests and the self-adhesive property negates the need to apply adhesive material to affix the present invention to a subject's body during use. As well, the need to apply electrically conductive paste to electrically conducting areas of electrodes becomes unnecessary.
A Patent, U.S. Pat. No. 5,331,959 to Imran, describes a low impedance dry conforming contact member in which are present rods or filaments which are cured into material such as a silicon-based material, such that when configured as an electrode provide impedance reducing projections which protrude into the pores of a subject's skin during use. Said rods or filaments reduce the need to use conductive paste. Another U.S. Pat. No. 4,524,087 to Engel, describes a conductive electrode application comprising an adhesive, swellable, dermally-nonirritating, conformable, ionic hydropolymer biomedical electrode fabricated by a claimed process.
Continuing, three Patents to Keusch et al, U.S. Pat. Nos. 4,706,680, 4,989,607 and 5,143,071 describe hydrogels which are caused to be highly conductive by the inclusion of an essentially uniformly distributed active electrolyte therein. Said Patents state that to form the hydrogels a polymeric mixture is caused to become cross-linked by exposure to radiant energy. This causes a gel-like solid to form which is sufficiently tacky and adhesive to adhere to subject's skin and which is substantially non-stringy and non-aggressive so that subject comfort is protected.
A Patent to Highe et al., U.S. Pat. No. 5,289,822 describes an electrode formed of a dry-conductive material having an outer surface for placement in contact with a subject's skin. A composition is deposited on at least a portion of the surface of the dry-electrode which comprises a plurality of water-containing vesicles. The purpose of said water-containing vesicles being to effect an immediate lowering of subject skin resistance upon the application of the electrode. It is stated that a period of approximately four minutes is otherwise required for moisture from a subject's skin to naturally occur at the electrode.
A Patent to Schmid, U.S. Pat. No. 5,124,107 describes a process for manufacturing a body electrode which comprises one or more galvanically active sensors which are combined with a first layer capable of adhering to a subject's skin, on a body contact side thereof. A second covering or supporting layer is also present on the opposite side of the body electrode. The process for manufacture provides that the two layers are sequentially cast in a mold which provides intended shape and size. The procedure avoids manufacturing problems encountered where electrodes are stamped from a preformed sheet. A potential problem of using such an electrode as provided by the Schmid 107 Patent is that it provides a laterally oriented conductive path between said galvanically active sensors through the first layer thereof. Electrically anisotropic conducting hydropolymers would be preferable.
Continuing, a Patent to Suyama et al, U.S. Pat. No. 5,132,058 describes a process for producing an anisotropically electroconductive sheet having a plurality of electroconductive portions extending in the direction of the thickness of the sheet. Application of an anisotropic magnetic field is utilized to draw electroconductive particles into a molding material such that said electroconductive particles gather where said electromagnetic field is applied. Another Patent which describes a similar system to that achieved by practice of the Suyama et al. Patent is U.S. Pat. No. 4,778,635 to Hechtman et al. A Patent to Kashiro et al., U.S. Pat. No. 4,209,481 describes an anisotropically electroconductive sheet in which electroconductive wires are formed into patterned groupings, which patterned groupings are in turn formed into patterns. The wires are parallel in the direction of the sheet thickness, and spaced apart by non-electroconductive elastomer. Another Patent, U.S. Pat. No. 5,045,249 to Jin et al., describes electrical interconnections made by means of a layer or sheet medium comprising chains of magnetically aligned, electrically conductive particles in a nonconducting medium. End particles of chains protrude from a surface of the medium to effect electrical contact. A Patent to Abraham et al. describes an electrode for use with electrosurgical apparatus which provides capacitive coupling with the skin of a subject. The electrode includes a conductive plate connected to the electrosurgical apparatus with an insulating layer disposed in contact with the conductive plate and on the opposite face of the insulator there is provided conductive material in the form of a plurality of discrete islands of conductive adhesive material which contact the skin of a subject during use. Another Patent, U.S. Pat. No. 5,232,639 to Reitz et al. describes a process for forming articles with anisotropic void distributions therein.
It is also established that electrode configuration can be important in determining the accuracy of monitored signals. For instance, the use of a Bulls-eye shaped electrode, which comprises a central electrode surrounded by one or more annular ring electrodes, can provide signals which focus upon a specific region of a subject's heart, which focus is not available when a simple electrode geometry is utilized. As well, Bulls-eye shaped electrodes allow determination of derivatives of detected signals in use.
An article by He et al. titled "Body Surface Laplacian Mapping of Cardiac Electrical Activity" published in The American J. of Cardiology, Vol. 70, Dec. 15, 1992 describes the use of Bulls-eye shaped electrodes to map derivatives of cardiogenic signals.
Patents which describe unusual geometrical electrode configurations are, for instance, a Patent to Clare et al., U.S. Pat. No. 5,295,482 which discloses a large surface area electrode in which a central portion is surrounded by two surrounding ring portions., said central and two surrounding ring portions being separated from one another by annular regions. This Patent states that during use current density is found to be greater at the outer edge of an electrode than it is at a more central location. The purpose of the described system is disclosed as being to effect a more uniform distribution of current density over the effective large surface area of the disclosed electrode during use, by providing multiple "outer-edge" providing portions. Other references which describe the "edge-effect" are a Patent to Dahl et al., U.S. Pat. No. 5,063,932 and a Canadian Patent No. 1,219,642. In addition, two articles also treat the subject, said articles being: "Optimal Electrode Designs for Electrosurgery, Defibrillation, and External Cardiac Pacing", by Kim et al., which appeared in Transactions On Biomedical Engineering, Vol. BME-33, No. 9, September 1986; and "Analysis and Control of the Dispersive Current Distribution under Circular Dispersive Electrodes", by Wiley and Webster, which appeared in the IEEE Transactions On Biomedical Engineering, Vol. BME-29, No. 5, in May 1982.
Even in view of the above cited literature, need remains for a convenient to utilize bioelectric interface which is suitable for application to subjects of differing body sizes, which bioelectric interface comprises equivalent Einthoven triangle limb electrodes on a common subject chest mounted support sheet, which preferably comprises an electrically anisotropic conducting hydropolymer self adhesive material, which provides electrodes of a geometry appropriate for optimizing electrical contact to a subject, which allows accurately monitored signals to be obtained therefrom during use, and which facilitates external cardiac pacing, cardiac defibrillation, electro surgery, electro-ablation processes, and impedance cardiography.